"Ideal" intensities of supersonic molecular beams

Abstract

A general equation is derived to predict ideal supersonic beam intensities, allowing for an ellipsoidal local speed distribution at the skimmer. With suitable approximations this is found to reduce to all of the previously derived results. A new approximate equation is presented. This can accurately reproduce the intensities predicted by the general equation, provided only that the speed ratio in the radial direction at the skimmer is much greater than 3/2. It is found that a relatively broad speed distribution in the radial direction can result in an increase in the centerline beam intensity. This increase is only weakly dependent on the nozzle–skimmer separation, and it decreases as the skimmer radius is increased.